Inlet and outlet valve rows alternate in a state-of-the-art internal combustion engine, that is, in the direction transverse to the longitudinal, a row of outlet valves is followed by a row of inlet valves, a row of outlet valves again, and lastly a row of inlet valves. Two camshafts are provided, an inlet camshaft and an outlet camshaft, which are positioned above the outer valve rows, and each of which actuates the valves of the outer valve row and the valves of the nonadjacent inner valve row. The valves of the inner valve rows are inevitably inclined at a steep angle to the longitudinal axes of the pertinent cylinders, this resulting in an unfavorable shape for the combustion chamber. Moreover, since the length of the inlet and outlet channels of the two cylinder rows varies, there is no certainty that the same admission and combustion conditions are present in all cylinders.
In order to prevent these unfavorable conditions, DE-A 38 31 333 discloses the mounting of inlet valve rows on both sides and near the plane of symmetry extending between the cylinder rows, but the outlet valve rows on the outside of the inlet valves, and provision of a common inlet camshaft for the two inlet valve rows in the plane of symmetry between cylinder rows and provision of an outlet camshaft for each outlet valve row.
As a result, all cylinders have combustion chambers, as well as inlet and outlet valves, of identical design, so that uniform admission and an identical combustion process for all cylinders are ensured. It has been found, however, that cylinder-selective fuel injection, essential for good mixture preparation, cannot be achieved with this internal combustion engine. In addition, intense heating of the intake mixture and the resulting admission loss are unavoidable. Lastly, this design cannot be used for an internal combustion engine with more than two inlet valves, since there is no room on the inlet camshaft common to all the inlet valves for more than two cams per cylinder. Because of these cramped space conditions, the inlet valves can be actuated only by tappets, not by rocker arms.